The present invention relates to systems for managing multi-layer communication networks. Embodiments of the present invention relate to a framework for mapping interconnections between layers of the multi-layer communication network (cross-layer mapping) and managing communication failures in the multi-layer network.
Decades ago, the rise in demand for telephony services spurred on the deployment of high capacity optical fiber networks. The subsequent rise in demand for Internet services resulted in leveraging of such optical networks for transmission of IP packets in an IP-over-Optical communication scheme. Such a multi-layer configuration utilizes the IP routers for controlling networking functions and the optical network for providing high throughput communication paths between the IP routers.
FIG. 1 illustrates an example of a multi-layer network which includes an Internet Protocol (IP) layer connected over an optical layer (e.g. Dense Wavelength Division Multiplexing—DWDM technology). Multi-layer networks can also include an additional a middle layer of Time division Multiplexing (TDM) switches, such as defined by Optical Transport Networking (OTN), or alternatively, a packet-optical or Ethernet layer instead of an IP layer.
Since such networks carry extremely large amounts of communication traffic, and are widely spread across multiple geographical locations, any connectivity failure at the IP or optical layers can impact a large amount of users. As such, multi-layer networks need to recover rapidly and efficiently from a failure in order to provide service continuity to the user.
In an IP-over-Optical multi-layer network, a link between routers of the IP layer (FIG. 1) is established by an optical path between optical switches (also referred to herein as optical routers or nodes) of the optical layer (FIG. 1). Failure of an optical path can be restored by rerouting the optical path around the failure (to restore connectivity between IP routers), while failure of an IP path can be restored by routing communication traffic through different IP routers.
There are several restoration framework types for recovering communication in an event of an optical and/or IP communication failure: (i) pure optical frameworks, in which the decision to restore optical paths is controlled by the optical layer; (ii) multi-layer frameworks that are biased towards use of distributed signaling to reroute optical connections at a time of a failure based on decisions taken in distributed fashion by the IP routers; and (iii) centrally controlled multi-layer frameworks which can reroute connections by instructing the router to re-signal the connection or by instructing the optical nodes to perform the reroute.
A pure optical framework can rapidly restore optical routing, however, the restoration path established by the optical layer may not meet the demands of the IP layer—for example its latency could be too high to be useful for the IP layer. In addition, optical restoration is only effective when the failure is in the optical domain and as such it does not take into account failures in the IP layer. Finally, when the optical failure is repaired and the system reverts to normal mode (working path), the switch from the restoration path to the repaired working path without coordination with the IP layer may result in unnecessary traffic outages.
A distributed multi-layer framework relies on signaling between the IP and optical layers and assumes that the IP router takes into account the constraints of optical connections, and is capable of negotiating these constraints with the optical layer should the most stringent constraints result in non-usable optical paths. This requires provisioning of multiple “path options” to the router, which creates a cumbersome process and a rigid negotiation process between the layers, which follows a fixed order of increasingly relaxed constraints irrespective of the actual failure. This is a time consuming process and creates churn since some restoration path options can be irrelevant to the actual failure. The distributed multi-layer framework also assumes that the decision to restore IP links via the optical layer is statically determined a-priori. In practice, some links could stay down without impacting traffic, while others must be restored on-the-fly, based on current traffic conditions. A distributed multi-layer framework poorly addresses multi-vendor networks, and multi-domain networks due to a lack of standards between vendors and networks.
A centrally controlled multi-layer framework is advantageous in that it can decide which connections to restore and how to restore them based on global understanding of the network and its current needs, however, it relies on the availability of the central controller, its site and server and the communications network to it and is thus more vulnerable. Lack of central controller availability can result in severe traffic loss and service contract violation. In addition, a centralized controller can experience signaling load and processing load during a large scale failure, causing slow recovery. Due to these limitations, network operators are reluctant to adopt multi-layer framework solutions.
In efforts of addressing the limitations of the above described restoration approaches, the present inventor has devised a framework for managing optical restoration without negatively impacting communication through the IP layer following restoration and following subsequent reversion to the working path.